Reactive mixing enables enzymatic depolymerization of recalcitrant or unsortable polyester wastes.

Area of Science:

• Polymer Science
• Chemical Engineering
• Sustainable Materials

Background:

• Enzyme-catalyzed depolymerization is effective for poly(ethylene terephthalate) (PET) due to its slow crystallization.
• Crystalline phases in polyesters hinder enzymatic hydrolysis, limiting recycling of materials like poly(butylene terephthalate) (PBT) and mixed or heterogeneous waste streams.

Purpose of the Study:

• To develop a method for enzymatic recycling of rapidly crystallizing and heterogeneous polyester wastes.
• To improve depolymerization yields for recalcitrant polyester materials by altering their crystallization properties.

Main Methods:

• Melt transesterification and vitrimerization of mixed polyester wastes, including PBT and PET nonwoven waste.
• Leveraging in-situ catalysts present in the waste streams.
• Reactive blending of incompatible polyester wastes to form processable copolyesters.

Main Results:

• Reactive blending produced copolyesters with significantly reduced crystallization rates.
• Depolymerization yields for mixed PET nonwoven and PBT waste increased from 20% and 1% to 90%.
• The developed method enables enzymatic recycling of previously unsortable and recalcitrant polyester waste streams.

Conclusions:

• Melt transesterification and vitrimerization offer a synergistic approach to overcome the limitations of enzymatic polyester recycling.
• This strategy effectively replaces material sorting, broadening the applicability of enzymatic recycling to diverse and challenging waste streams.
• The process enhances the sustainability of polyester waste management by enabling the valorization of complex waste mixtures.